Linear actuator primarily uses an electric motor and a driving component such as a worm shaft and a worm wheel to drive and rotate a lead screw, while the lead screw is provided for driving a telescopic tube threadedly connected thereon to perform a linear extension or retraction with respect to an outer tube of the telescopic tube. Since the structure, installation and other conditions are simpler and more convenient than those of pneumatic and hydraulic cylinders, the linear actuator is used extensively for equipments such as hospital beds and electric chairs or any other areas requiring extensions and retractions.
For safety purpose, a linear actuator generally comes with limit switches installed in the outer tube and at positions corresponding to inner and outer limit positions of a moving path inside and outside the telescopic tube respectively, such that the limit switches are electrically coupled to the electric motor for controlling the ON/OFF of the electric motor and preventing any cleavage or damage to the transmission components caused by improper extension or retraction of telescopic tube. In addition, the limit switches can be installed at starting and ending positions of the path only, so that when the linear actuator is applied to equipments such as an electric chair, there is no safety measure provided at positions other than the starting and ending positions of the moving path, and children may be clamped or injured accidentally by the electric chair. Obviously, the conventional linear actuators require improvements.